A turbine engine has a compressor section, a combustor section and a turbine section. In operation, the compressor section can induct ambient air and compress it. The compressed air can enter the combustor section and can be distributed to each of the combustors therein. FIG. 1 shows one example of a known combustor 10. The combustor 10 can include a pilot swirler 12 (or more generally, a pilot burner). A plurality of main swirlers 14 can be arranged circumferentially about the pilot swirler 12. Fuel is supplied to the pilot swirler 12 and separately to the plurality of main swirlers 14 by fuel supply nozzles (not shown). When the compressed air 16 enters the combustor 10, it is mixed with fuel in the pilot swirler 12 as well as in the surrounding main swirlers 14. Combustion of the air-fuel mixture occurs downstream of the swirlers 12, 14 in a combustion zone 20, which can be largely enclosed within a combustor liner 22. As a result, a hot working gas 23 is formed. The hot working gas 23 can be routed to the turbine section, where the gas can expand and generate power that can drive a rotor.
During engine operation, acoustic pressure oscillations at undesirable frequencies can develop in the combustor section due to, for example, burning rate fluctuations inside the combustor section. Such pressure oscillations can damage components in the combustor section. To avoid such damage, one or more acoustic damping devices can be associated with the combustor section of a turbine engine. One commonly used acoustic damping device is a resonator 24, which can be a Helmholtz resonator. Various examples of Helmholtz resonators are disclosed in U.S. Pat. Nos. 6,530,221 and 7,080,514. Generally, a resonator 24 can be formed by attaching a resonator box 26 to a surface of a combustor section component, such as an outer peripheral surface 28 of the combustor liner 22. A plurality of resonators 24 can be aligned circumferentially about the liner 22.
Each resonator 24 can be tuned to provide damping at a desired frequency or across a range of frequencies. A radially outer wall 30 of the resonator box 26 can include a plurality of holes 32 therein. Further, the liner 22 can be perforated with holes 38. Each resonator box 26 is welded to the liner 22 around a group 39 of the holes 38. Air enters an internal cavity of the resonator 24 through the holes 32 in the radially outer wall 30 of the resonator box 26. The internal cavity is formed between the resonator box 26 and the liner 22. The air can exit the resonator 24 by flowing through the holes 38 in the liner 22. In this way, air can purge an internal cavity and can prevent the ingestion of hot gases 23 from within the liner 54 into the resonator 50.
In addition to acoustic damping, the resonators 24 can serve an important cooling function. For instance, air passing through the holes 32 can directly impinge on the hot surface of the liner 22, thereby providing impingement cooling to the liner 22. In addition, the air exiting the resonator 24 through holes 38 in the liner 22 can provide a film cooling effect on the inner peripheral surface 40 of the liner 22.
However, the effectiveness of such cooling flows is limited primarily to the portion of the liner 22 enclosed by the resonator box 26. The portions of the liner 22 downstream thereof are not effectively cooled, despite such area being subjected to some of the highest heat loads. Further, the greater the amount of air that is used for cooling the liner, the greater the loss in engine efficiency and an emissions penalty is incurred, as there will be greater amounts of NOx in the turbine exhaust.
Thus, there is a need for a system that can minimize such concerns.